What is it?

The ketogenic diet is a very low-carbohydrate, moderate-protein and high-fat diet. It typically contains 75% fat, 20% protein and 5% carbohydrates, although slight variances are common. The basis of the diet is that any food containing a significant amount of carbohydrates should be avoided. This leads to complete restriction of sugary foods, grains, cereals, starches, fruits, beans, legumes and sauces. An individual’s meals become primarily based around meat, fish, eggs, butter, cheese, nuts, oils, avocados, low-carb vegetables, herbs and spices.

But why?

The body runs off a molecule called Adenosine triphosphate (ATP), which stores and supplies energy to every cell in the body. ATP is created by the metabolic process called aerobic respiration, where glucose is converted into ATP through multiple metabolic pathways. Carbohydrates, such as sugar and starch, for example, are readily broken down into glucose, the body’s principal energy source.

The physiological benefit to the ketogenic style of eating is based upon reducing glucose and insulin production, so the body switches to a ketone-dependent fuel source. Ketosis is a natural process the body initiates to help us survive when food intake is low, and also occurs when glucose availability is scarce. During this state, we produce ketones, either from the breakdown of dietary fat or from stored body fat. In other words, ketones are the “backup” energy source when glucose isn’t available for energy production.

What are the proposed physiological benefits of being in ketosis?

Advocates of ketogenic diets will promote that being in ketosis will lead to significantly less insulin production, a fat-storage hormone, due to insulin levels being primarily dictated by carbohydrate intake. Lower circulating insulin will therefore lead to less fat storage from an individual’s energy intake.

Ketosis will also allow an individual to use their own body fat for energy production, as opposed to relying on carbohydrates and glucose to burn off as fuel. In turn, it can be seen as a method in which to shed excess weight by altering your source of energy use.

The Benefits

  • It can work for weight loss, but not for the reasons advertised – The ketogenic diet is a successful method in which to indirectly create a caloric deficit. As calories come from 3 different nutrients, protein, carbohydrates, and fat, abstaining from the intake of one of these calorie sources will tend to cause a lower caloric intake. Simple logic. Nearly all scientific studies that put subjects on a ketogenic diet notice weight loss:

6.9kg loss after 3 months [1]

6.8% loss of total body weight after 3 months [2]

5.8kg loss after 6 months [3]

9.4kg loss after 24 weeks [4]

6.8kg loss after 10 weeks [5]

4.2kg loss after 6 weeks [6]

It should be noted that in most studies comparing weight loss of low-carbohydrate diets versus low-fat diets, weight loss will be more dramatic in the low-carbohydrate group in most circumstances. However, this is due to a larger reduction in water storage from a low-carbohydrate diet, as opposed to an increased loss of actual tissue weight, and will be regained when carbohydrates are introduced back into the diet (known as “water weight rebound”).

  • More stable blood sugar and energy levels – Deterring away from carbohydrate and sugar rich meals may allow for a more stable flow of energy throughout the day, with less blood glucose spikes and crashes. It may also be of benefit for diabetics looking to have more control over their blood glucose levels. Prevention of diabetes onset might also be a benefit to stabilising blood sugar levels, as frequent high blood sugar spikes, combined with high insulin levels (and lack of exercise) is known to eventually cause cells to lose their responsiveness and become insulin resistant, leading to type II diabetes.
  • Removal of processed sugar – Despite sugar, specifically fructose, not necessarily having damaging effects in moderate quantities, it is still a health benefit to follow a diet that eliminates their intake. Mechanistic studies convey that the metabolism of fructose generates substrate for de novo lipogenesis that may lead to the accumulation of triglycerides in the liver, as well as causing high uric acid levels that impact negatively on kidney function [7]. A meta-analysis of epidemiological data also provides evidence that over consumption of sugar increases the risk factors for cardiovascular disease and metabolic syndrome [8].

The Cons

  • Unnecessary food restrictions – As much as advocates of the diet try to demonize carbohydrates and insulin production, this is not an issue based on scientific evidence. Insulin is a fat-storing hormone, but it can only store fat with excess energy, and therefore is only an issue if you are consuming too many calories relative to your daily energy expenditure. In addition, despite common belief, carbohydrates do not magically convert into body fat unless an energy surplus is maintained. Even with an excess of energy, carbohydrates convert to fat at a rate of only 5-25% [9][10][11], in comparison to a near 100% conversion of dietary fat into body fat. Based on this, avoiding carbohydrates is not a necessary step for weight loss, but can be a utilised tool that suits some individual’s lifestyle and habits.
    Avoidance of fruits, grains, starches, beans and legumes also makes it harder to access essential nutrients such as magnesium, copper, phosphorus, zinc, phytonutrients, vitamin C, and antioxidants. Non-essential but protective chemicals such as lignans, phytic acid, saponins, phytosterols and phenolic compounds are also only found mainly in wholegrain products.
  • Lack of dietary fiber – A large percentage of one’s fiber intake is due to the consumption of fruits, grains and starches. Removing these products from your diet leaves you solely dependent on green vegetables for your daily fiber intake, which is recommended to be 30 grams per day. Dietary fibre is known to resist digestion in the small intestine and reach the colon so they are fermented by the gut microflora, where changes in the composition and activity of the gastrointestinal microflora benefits many aspects of one’s health and prevents certain diseases [12].
  • Does not prepare for weight loss plateaus – Like any restrictive plan, weight loss will initially occur but after a certain time period the body will adapt to a reduced energy intake and progress will stall. The only way to continue progress is to purposefully track and reduce energy intake to continue ensuring a deficit of energy and maintaining a negative energy balance. However, although a ketogenic diet usually indirectly causes an energy deficit, it does not track caloric intake and so it is harder to adjust when progress stalls. Portion sizes can be subjectively reduced, and this may be successful, but continuation of fat loss is not guaranteed unless calories are tracked.
  • Reduced strength and power performance – High-intensity performance, mainly regarding gym or sports exercise, relies heavily on glucose and glycogen availability within muscle tissue to be able to quickly produce ATP for strength and power. Substrate utilization in an individual is dependent on the interaction between exercise intensity-induced responses (which increase carbohydrate utilization) and endurance training-induced responses (which promote lipid oxidation). When free fatty acids are oxidized, the maximum rate of ATP resynthesis is about 0.40 moL/min, while an aerobic or anaerobic breakdown of glycogen (carbohydrates) can generate from 1.0 to 2.0 mol of ATP/min [12][13], clearly the superior option. This can negatively affect muscular fatigue in high-intensity exercise, and may be of great importance to athletes or fitness enthusiasts.

Who should run this diet?

The Ketogenic diet is ideal for someone with excess weight who is looking for a simple, restrictive eating plan that will likely strip weight at a fast rate for the first few months. Those looking to make slight improvements to their diet by removing processed and sugary foods may also wish to follow this diet, as it can promote greater health compared to the average western diet. Diabetics or those looking to control blood glucose levels should also look towards analysing and switching to a Ketogenic diet to try and help current or potential issues related to insulin production.

The Ketogenic diet is not ideal for people who are not willing to follow a restrictive eating plan regarding food choices, as a plan such as IIFYM would be more beneficial. Health enthusiasts who do not want to restrict their access to certain micronutrients, phytonutrients and antioxidants may also want to look elsewhere. Athletes or resistance trainees would also not want to deter away from an adequate carbohydrate intake as their performance may suffer due to reduced muscular energy availability.


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